The present invention relates to a thermal spraying method for increasing adhesion strength of the thermal sprayed layer. The present invention relates to a thermal spraying apparatus and a powder passage apparatus which can be used in the thermal spraying method.
There has been developed a thermal spraying method for forming thermal sprayed layer in the industrial world. In the thermal spraying method, material having a powder shape is heated in high temperatures, the heated material is sprayed and is piled up on a surface of an object by thermal spraying. The thermal spraying advantageously increases abrasion resistance and corrosion resistance of the object by the thermal sprayed layer. Also, Japanese Unexamined Patent Publications 63-66900 and 5-5893 disclose a thermal spraying method which uses: an energy source for flying material; and another energy source for heating the material by a laser beam and being independent of the energy source. According to this Publication techniques, the material for thermal spraying flys to the object, and the flying material is heated by the laser beam running parallel with the surface of the object.
In the conventional thermal spraying method, the heated material for thermal spraying decreases in flying speed as it approaches the object. Also, in the thermal spraying method concerning the above-mentioned Publications, the heated material for thermal spraying decreases in flying speed as it approaches the object. Therefore, the thermal spraying layer is not much improved in adhesion strength, even when other spraying conditions are improved.
The present invention has been accomplished in view of the aforementioned circumstances. It is therefore an aim of the present invention to provide a thermal spraying method for improving adhesion strength of a thermal sprayed layer. It is therefore another aim of the present invention to provide a thermal spraying apparatus for using the present invention method and for improving adhesion strength of a thermal sprayed layer. Also, it is therefore still another aim of the present invention to provide a powder passage apparatus which can be used in carrying out the present invention method and can suppress powder material from being stopped in a passage.
According to a first aspect of the present invention, a thermal spraying method for producing a thermal sprayed layer by heating material for thermal spraying, by flying the heated material or the heating material to a surface of an object, and by piling the heated material on the surface of the object, comprises the steps of:
(1) preparing a speed-increasing means for adding energy to the heated material or the heating material to increase a flying speed of the material; and
(2) adding energy to the heated material or the heating material by the speed-increasing means in such a manner that a flying speed of the heated material or the heating material increases until the material reaches the surface of the object.
According to a second aspect of the present invention, a thermal spraying apparatus for producing a thermal sprayed layer by heating material for thermal spraying, by flying the heated material or the heating material to a surface of an object, and by piling the heated material on the surface of the object, comprises:
(1) a passage-forming member for forming a passage through which material for thermal spraying passes;
(2) a heating means for heating the material passing through the passage-forming member or discharged from the passage-forming member; and
(3) a speed-increasing means for increasing a flying speed of heated material.
According to a third aspect of the present invention, a powder passage apparatus comprises:
(1) a conductive coil having conductivity, and having an axis and a plurality of loops disposed substantially coaxially with respect to the axis; and
(2) a passage-forming member disposed along the axis of the conductive coil for supplying material for thermal spraying.
According to the first aspect of the present invention, until the heated material reaches the surface of the object, energy is added to the heated material or the heating material by the speed-increasing means in such a manner that a flying speed of the heated material increases. Accordingly, the material for thermal spraying collides against the object at a high speed. So, the thermal sprayed layer is improved in adhesion strength.
Also, in a preferable mode, the flying speed of the material is increased in comparison with that of heating position. In other words, in a preferable mode, the flying speed of the material at the heating position, namely, the flying speed before the acceleration, is lower than that of the material after the acceleration. This mode can lengthen the time for heating the material for thermal spraying, thereby enhancing ability for heating the material for thermal spraying to high temperatures.
According to the second aspect of the present invention, a thermal spraying apparatus comprises: (1) a passage-forming member for forming a passage through which material for thermal spraying passes; (2) a heating means for heating the material passing through the passage-forming member or discharged from the passage-forming member; and (3) a speed-increasing means for increasing a flying speed of material. So, the thermal spraying apparatus according to the second aspect can be used in carrying out the first aspect of the present invention, thermal spraying method. Accordingly, the material for thermal spraying collides against the object at a high speed, and the thermal sprayed layer is improved in adhesion strength. Preferably, the speed-increasing means increases the flying speed of the material than that of the material during heating.
According to the third aspect of the present invention, the powder passage apparatus comprises: a conductive coil, having conductivity, and having an axis and a plurality of loops disposed substantially coaxially with respect to the axis. Also, the passage-forming member is disposed along the axis of the conductive coil. So, the apparatus according to the third aspect can be used in heating the material for thermal spraying by means of induction heating. Induction heating is advantageous in heating the material for thermal spraying in a short time, and in controlling heating temperature.
Further, according to the third aspect of the present invention, when electricity is supplied to the conductive coil, it is suppressed that the material for thermal spraying adheres to the inner surface of the passage of the passage-forming member. The reason is as follows: The conductive coil generates magnetic force along the central axis line of the passage, namely, along the central axis line of the conductive coil. So, the powder material for thermal spraying, having permeability, easily flows along the center portion in a radial direction of the passage.
According to the first aspect of the present invention, until the heated material reaches the surface of the object, energy is added to the flying material by a speed-increasing means in such a manner that a flying speed of the material increases. When the flying speed of the material for thermal spraying is increased, the material collides against the object at a high speed, adhesion of the material is improved, and the thermal sprayed layer is improved in adhesion strength.
According to the preferable mode of this invention, the adding of the energy for increasing the flying speed of material is carried out after the heating of the material. That is to say, after the material for thermal spraying is heated, the flying speed of the material is increased. The heating before increasing the flying speed of the material can lengthen the time which is required for heating the material.
Or, according to the thermal spraying method for concerning another preferable mode of the first invention, the flying speed of the material can be increased during the heating of material. Also, the thermal spraying method concerning the first invention rarely allows the flying speed of the material to be increased before the heating of material.
The material for thermal spraying may be in a form of particle, when it flies to the object. The flying form of particle may be in a solid form, in a melting form, or in a partially melting form. The form of material before thermal spraying may be in a powder state, in a wire state, or in a rod state. When the form of material is powder, the average diameter of particle of the material is decided on occasion. The upper limit of average diameter of the particle may be for example 100 xcexcm, 200 xcexcm, 300 xcexcm or 500 xcexcm. The lower limit of average diameter of the particle is for example 1 xcexcm, 10 xcexcm or 40 xcexcm. Therefore, the average diameter of particle of the material may be in a range of 1-500 xcexcm, in a range of 10-300 xcexcm, or in a range of 40-200 xcexcm. The average diameter of particle is not limited within these.
The material for thermal spraying is preferably metal, especially metal powder. When the material for thermal spraying is metal, it has conductivity. Also, many metals have good magnetic permeability. The metal may have, in the ordinary temperature range, ferromagnetism or paramagnetism. Concretely, the metal constituting the material for thermal spraying may be ferrous such as cast iron, carbon steel, stainless steel, or alloy steel. Also, the metal constituting the material for thermal spraying may be non-ferrousxe2x80x94at least one selected from the group consisting of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, or titanium alloy. Sometimes, the material for thermal spraying may be ceramics, cermet mixing ceramics with metal. Ceramics may be oxide, nitride, carbide or boride. Ceramics may be at least one selected from the group consisting of alumina, silica, magnesia, silicon carbide, silicon nitride, boride titanium and so on. Even when the material for thermal spraying is formed of ceramics, until the material reaches the object, the energy is given to the material in such a manner that the flying speed of the material is increased, impact speed of the material is increased, and the material collides against the object at a high speed. Therefore, the thermal sprayed layer is advantageously improved in adhesion strength.
When the material for thermal spraying is formed of ceramics, the induction heating is not obtained in the material unlike metal. For ceramics does not have conductivity substantially. In case where the passage through which the material for thermal spraying passes is formed of carbon tube, the carbon tube can be heated by induction heating, and the material for thermal spraying in the carbon tube is heated by radiant heat from the carbon tube.
According to a preferable mode, the heating of material is carried out by a first energy source, and the adding of energy for increasing the flying speed of material is carried out by a second energy source. Also, according to another preferable mode, the first energy source have one path and another path for transmitting energy thereof, the heating of material is carried out by the one path of the first energy source, and the adding of energy for increasing the flying speed of the material is carried out by the another path of the first energy source. The first energy source is not restricted in kinds. So, the first energy source can be a flame-generating means for generating a flame of fuel (acetylene and propane, etc.)-oxygen, a plasma-flame generating means for generating a plasma flame, a laser means for generating a laser beam, or an induction heating means for heating the material for thermal spraying by induction heating. The induction heating means includes the case in which the passage or the passage-forming member is induction-heated and the material is heated by radiant heat of the heated passage or the heated passage-forming member.
The present invention permits the case in which the heating of the material for thermal spraying is carried out by using the first energy source, and the increasing of flying speed of the material for thermal spraying is carried out by using the second energy sources unlike the first energy source. This case allows the first energy source and the second energy source to be controlled independently and individually. So, this case allows the heating of material and the increasing of the flying speed of material to be controlled independently and individually. Therefore, this case can enlarge an adjustable range in temperature and flying speed of the material for thermal spraying. Accordingly, this case can select a mode in which the temperature of material is high and the flying speed of material is high, another mode in which the temperature of material is low and the flying speed of material is high, or still another mode in which the temperature of material is high and the flying speed of material is low.
The present invention permits the case in which the heating of material is carried out by the one path of the first energy source, and the adding of energy for increasing the flying speed of material is carried out by the another path of the first energy source. This case allows the heating of material and the increasing of flying speed of the material to be controlled. This case can enlarge an adjustable range in temperature and flying speed of the material for thermal spraying.
The first energy source is not restricted in kinds for heating the material. The first energy source can be a flame-generating means for generating a flame of fuel (acetylene and propane)-oxygen, a plasma-flame generating means for generating a plasma flame, or a laser means for generating a laser beam. In a preferable mode, a material for thermal spraying has conductivity and magnetic permeability, and the first energy source may be constituted by an induction heating means for heating the material for thermal spraying. The induction heating means can control the degree of heating of the materialxe2x80x94low temperature, medium temperature or high temperaturexe2x80x94by adjusting frequencies of alternating current, current value, electric power, etc. The speed-increasing means may be a means which uses a swelling gas pressure obtained by expanding gas or by evaporating liquid in short timexe2x80x94for example, by evaporating liquid with the laser beam.
Thermal spraying apparatus concerning the second aspect includes: (1) a passage-forming member for forming a passage through which the material for thermal spraying passes; (2) a heating means for heating the material passing through the passage-forming member or discharged from the passage-forming member; and (3) a speed-increasing means for adding energy to the material for thermal spraying to increase a flying speed of the material and to accelerate the flying speed of the material. The speed-increasing means may increase the flying speed of the material than that of the material during heating. The heating means for concerning the thermal spraying apparatus of the second aspect may be a flame-generating means for generating flame of fuel (acetylene and propane)-oxygen, a plasma flame generating means for generating plasma flame, a laser means for generating a laser beam, or an induction heating means for heating the material for thermal spraying.
The thermal spraying apparatus concerning the above mentioned second aspect can be used in carrying out the first aspect of the present invention method, increasing the flying speed of the material for thermal spraying.
The powder passage apparatus concerning the third aspect comprises: (1) a conductive coil having conductivity and having an axis and a plurality of loops disposed substantially coaxially with respect to the axis; and (2) a passage-forming member disposed along the axis of the conductive coil for supplying material for thermal spraying.
According to the powder passage apparatus concerning the third aspect, when powder material has magnetic permeability, it is suppressed that the powder material for thermal spraying adheres to the inner surface of the passage of the passage-forming member. The reason is as follows: when current is supplied to the conductive coil, the conductive coil generates magnetic force along the central axis line of the conductive coil. So, the powder material for thermal spraying, having magnetic permeability, easily flows along the center portion in a radial direction of passage under the influence of the magnetic force. In the case where the material for thermal spraying is powder, when the powder passage apparatus concerning the third aspect is used as a powder passage apparatus of the thermal spraying apparatus, it is suppressed that the powder material for thermal spraying adheres to the inner surface of the passage. Therefore, this can suppress abnormal blockage of the material for thermal spraying in the passage. So, this can suppress inequality in heating the powder material for thermal spraying. Thus, the powder material for thermal spraying is uniformly heated as much as possible to high temperature, and the thermal sprayed layer is advantageously improved in adhesion strength.